What must an instructor endorse prior to a student's first solo flight?

Prior to a student's first solo flight, it is essential for an instructor to endorse the student's logbook and pilot certificate. This endorsement serves as a confirmation that the instructor has determined the student has the requisite knowledge, skills, and competencies to conduct a solo flight safely.

The logbook will typically record the endorsement, indicating that the instructor has evaluated the student’s abilities and deemed them prepared for solo flight, which is a pivotal milestone in flight training. The endorsement also acts as a legal requirement for the student to exercise solo privileges under FAA regulations, ensuring that the flight is conducted under supervision and with proper authorization.

Other options, while relevant to flight training, do not fulfill the regulatory requirements. Endorsing a flight log and pilot's manual, providing a weather briefing, or endorsing a flight school’s policy document are not mandated for solo flight and do not serve the purpose of documenting the instructor’s authorization for the student's solo flying privileges. Thus, it is the logbook and pilot certificate endorsement that is critical and necessary before a student can solo.